In mobile tree handling machines capable of moving in terrain, usually a cross-cutting saw is used, in which a chain-formed blade encircles the guide bar. The chain is moved by a motor which is in a power transmitting connection with it, and is usually controlled by pressure medium, such as hydraulic oil. To perform the cross-cutting the guide bar is turned against a tree by means of a cylinder, which is also controlled by pressure medium. In prior art cross-cutting saws of tree handling machines, the feeding speed of the guide bar and the feeding power are usually set to be constant. Thus, the feeding speed and the feeding power has to be adjusted so low that the cross-cutting saw can also saw trees with a high sawing resistance, for example when sawing thick trees. However, at the beginning of the sawing and when sawing thin trees, the feeding speed is too slow, which in turn retards the cutting of tree. In the final phase of the sawing the sawing speed remains slow, which easily causes crack damage in the tree.
At present, cross-cutting saws are known in which it the feeding pressure of pressure medium passing to the motor of the saw is measured, alkyd an attempt to keep it constant, wherein the rotational speed of the saw is kept substantially constant. In such systems, considerable and sudden stress may be directed to the saw if there exists significant variations in sawing resistance when cutting tree. This may even damage the cross-cutting saw. Prior art systems have poor efficiency, because the adjusting is performed through loss adjustment implemented by choking.